Dehydration of formamide to produce hydrocyanic acid



June 2, 1936. H. A. BOND ET AL 2,042,451

DEHYDRATION OF FORMAMIDE TO PRODUCE HYDROCYANIC ACID Filed April 12, 1933 INVENTORS- Her/an A. 50/20. and Norman 0. Scan.

ATTORNEY Patented June 2, 1936 UNITED- STATES PATENT OFFICE DEHYDRATION OI FOBMAMDE TO PRO- DUCE HYDROGYANIC ACID Harlan A. Bond and Norman D. Scott, Niagara Falls, N. Y., assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application A]!!! 12, 1933, Serial No. 865,752

I Claims. (Cl. 23-451) from the point where the reaction takes place to prevent the formation of localized heating which has various adverse effects, e. g., destruc-.

tion of the efliciency of the catalyst, thermal decomposition of reactants and/or products or the occurrence of undesirable side reactions. when the catalyst employed is a poor conductor of heat, for instance as in the case of metal oxides, the proper heat exchange is diflicult to accomplish.

An object of this invention is to provide for emcient heat transfer between the contact bodies and the exterior of the reaction vessel utilizing metal oxides as catalysts. Other objects will be hereinafter apparent.

These objects are attained according to our invention by providing a thin adherent coating of catalytic oxide on metal surfaces which metal surfaces are utilized for heat exchange.

The accompanying drawing, which illustrates one form of apparatus suitable for carrying out the invention, is described hereinafter in connection with one of the specific applications of the invention.

Our invention is directed to the catalytic dehydration of formamide to produce hydrocyanic acid. This reaction is highly endothermic and hence requires that the heat input be rapid. Furthermore, this reaction requires that the passage of the formamide through the reaction space be rapid in order to avoid undue exposure of the formamide and the reaction products to high temperatures in order to avoid excessive decomposition and/or undesirable side reactions. For these reasons the heat input to the reaction must be as rapid as possible in order to obtain good yields of hydrocyanic acid. Hereto fore it has been proposed to pass formamide through a narrow reaction space the walls of which are formed of a catalytic reaction material, for example, a reaction space may be made of brass and having such dimensions that no part of the gas flowing therethrough will at any time be more than inch from the catalytic metal surfaces which are supplying heat to the reaction. This method has been found satisfactory in effecting a rapid heat input to the catalytic surface where the reaction takes place. However, we have now discovered that certain metal oxides are superior to brass or other catalytic metal for this reaction. However, as pointed out above, the use of oxides as practised in the past introduces various difficulties in obtaining eiiicient heat exchange between the point of reaction and the exterior of the reaction vessel.

We have found that by dehydrating formamide in a narrow'reaction space made of metal, the

interior walls of which are coated with a thin,

adherent layer of catalytic oxide, the catalytic effect is markedly increased with substantially no sacrifice of heat exchange efliciency. This method results in increased yields of hydrocyanicacid and a decrease of undesirable side reactions.

The coating of catalytic oxide on the interior of a metal reaction vessel may be obtained by first coating the surface with a suitable metal, for instance by electroplating and then passing oxygen or air through the reaction vessel at a temperature suitable to eifect oxidation. The oxidation may be complete or partial as desired; we prefer to oxidize so as to obtain a continuous fllm of a thin adherent oxidized coating. Various other methods of obtaining the oxidized coating will be apparent to persons skilled in the chemical art. In place of electroplating, the metal whose oxides it is desired to produce may be coated by hot dipping methods or by painting with metal paint, 1. e. a suspension of finely divided metal in a suitable liquid. In some cases it may be desirable to construct the reaction vessel of v the metal whose oxide is desired and obtain the oxidized coating by superficial oxidation of the interior of the vessel. For instance, a brass vessel may be thus treated to produce a coating of zinc and copper oxides. In some cases it is possible to treat alloys such as brass so that the oxide layer produced by surface oxidation contains the oxides of the constituent metals in a ratio differing from the alloy composition. For instance, if a brass surface is heated to 400-650'. C. in an oxidizing atmosphere, a small amount of zinc distills to the surface, with the result that the proportion of zinc oxide in the oxide coating formed is greater than theproportion of zinc in the brass. We have found, however, that in the case of the dehydration of formamide to hydrocyanic acid, a coating free from copper oxide is preferable, since copper oxide apparently tends to catalyze undesired side reactions. Other methods of obtaining coated oxide coatings may be used; for instance, in order to obtain a coating of aluminum oxide the process known as calorizing may be employed. 'Many catalytic reactions occur in the presence of gases which have the property of reducing oxides to metal.

known as calorizing" afterwhich the tube and rod were led to form the reaction space. Each of these reaction chambers was then assembled in a furnace and formamide vapor 5 passed through at a suitable reaction tempera- Some of the oxides employed in our invention ture. The of! gases were passed into an alkaline may be non-reducible under such conditions; solution and the amount of hydrocyanic acid others may be reducible or partially reducible. formed was determined by determining the If during the reaction such reduction 0! the cyanide formed in the solution. The following oxides occurs, the catalytic activity may be reoxide coatings were used: 10 stored by interrupting the process and passing Zinc aside (on brass) z-Electroplated layer through air or oxygen at an oxidizing temperaof zinc, 0.001" thick, oxidized at 450-500" C. with ture. air.

We have found that the oxides of zinc, man- Aluminum oxide (on brass) :-A single coat of ganese, aluminum, chromium and tin are eflecaluminum paint, dried and then oxidized at 15 tive for the catalytic dehydration of formamide 500-600" C. with air. to produce hydrocyanic acid in high yields. 'In Aluminum oxide (on iron) :--Iron surface carrying out this reaction according to our incalorized" by heating in contact with a mixture vention, we prefer to use a reaction space havof aluminum and aluminum oxide at 900 C.

ing such dimensions that no part of the gas The calorized" surface was oxidized at 600 C. 20

passing therethrough will be at any time more with air. than one-half inch distant from the catalytic Manguneseoxidemn brass) z-Electrodeposited surface and to pass the gas through the apparamixture of manganese and manganese oxide, tus at a high rate of flow. The reaction may be oxidized at 500-600 C. with oxygen.

carried out with good results at temperatures Chromium oxide (on brass) z-Electroplated .25 between 400 and 650 C. We prefer to operate chromium, oxidized with oxygen for two hours over the range between 575 and 630 C. The at 600-630 C. rate of the flow of the gas mixture may be varied Tin oxide (on brass) :E1ectroplated layer over a considerable range with good results, de- 0.001" thick, oxidized at 500550 C. with air.

7 pending mainly upon thief :gnstrucfiion oi the ap- 'illlistfolloxiwidng results were obtained with these 30- paratus. For instance, e gas as a ong 5- ca a c o e' layers: tance to travel the rate or flow should be correspondingly increased. If the rate of flow is too slow,- some or the hydrocyanic acid formed may Fmmmlde Reaction peroento! be decomposed, while with an excessively high 15ml fig-Q1323? 35 rate of flow, some of the formamide may pass toHON through unreacted. In any case the optimum rate of flow may be ascertained by simple trials.- Voluma Referring to the drawing, I is a cylindrical metal zinc on m 40 tube shown in vertical section, with closures 2 Aluminum oxide 015x335: 5,000 565-680 85 40 and a at either end, equipped with inlet and fifi gggggm We fl g gg outlet connections 4 and Ii respectively. Inside Chromiumoxldn 30 1 0 of tubel is a cylindrical rod 6, shown in cross- Tm 7H6 section above the broken line and in elevation below the broken line. Into rod 6 is cut a wide m fiffi fg f'g gififig g ma g 5 spiral groove I to form a helical bafiie 8, which normal tempmtureand pnmn. fits closely into tube I. The interior surface our mvehum maybe utilized o carry out of the tube I and the exterior surface of the W5 catalytic reactions utilizing metal oxides or trodi I; are coated with the desired catalytic mamixtures of oxides as catalysts. For example 1f 50 er a a mlxtm-e e jre In operating the apparatus, the tube assembly metal a gg z i g g z f; :23 is heated to the desired temperature by any suitthe alloy oxidized m the W wan our mvem able means, e. g. an electric furnace; the reaction is meted to e coating of the interior tion gases are admitted through inlet connection walls or a reaction vessel but may he applied to 4, whence they follow the path of the spiral the surfaces or variously shaped metal parts 55 groove I, passing between the two catalytic 'surwhich my be inserted in the reaction space For itiiitgt ifiiiiffifiiliitff 5 g ig gf g i The following example illustrates the use of g; onde g i g s g gg g m our invention for the production of hydrocyanic as contact masses f a catalytic reaction in a 60 acid by the dehydration of formamide. reaction chamben Eagamplg An advantage of our invention is that it pro- A number of reaction chambers of the type ga g z z iggfig g ziigg g 3 1 1: 5 shown in the accompanying drawing were prewhich themtmn occurs Hence it ma p0 55 H i y be used pared, the spiral grooves on the rods 6 being 5', both to cool the Contact mass used for an deep by 1" wide. Five such reaction chambers othermlc catalytic reaction or to supply heat for were made of brass and one of iron. The tube d them My t1 and grooved rod of each brass reaction chamber an en 0 c i 0 mac Another were each coated with a thin layer of metal as vantage is that it i a mement means 70 indicated below; the rod then was assembled infor obtaining a large surface catalytic x1de side the tube and air was passed through at the materials a metal reactmn apparatus- A temperatures indicated to oxidize the coated ther advantage is that it provides a means for obmetal. The surfaces of the iron tube and rod taming improved yi in the hydration of were coated with aluminum oxide by the process i rm mi e o hydrocyanic acid. 75

We claim:

1. A process for eflecting the catalytic formation of hydrocyanic acid comprising passing i'ormamide over a heated metal surface having a thin adherent coating of a catalytic oxide formed by oxidizing an adherent fllm of a metal selected from the group consisting oi! zinc, aluminum, manganese, chromium, and tin.

2. A process for eflfecting the catalytic formation of hydrocyanic acid comprising passing iormamide over a heated metal surface having an adherent coating of zinc oxide formed by oxidizing an alherent fllm oi zinc.

3. A process for eflecting the catalytic formation of hydrocyanic acid comprising formamide through a heated metal reaction chamher with inner walls having a thin adherent coating of an oxide formed by oxidizing an adherent metal film of a metal selected from the group consisting of zinc, aluminum, manganese, chromium, and tin, the dimensions of said chamber being such that no portion of said iormamide will be more than one-half inch distant from said inner walls.

4. A process for efiecting the catalytic formation of hydrocyani'c acid comprising passing iormamide through a heated brass reaction chamher with inner walls having an adherent coating of zinc oxide formed by oxidizing zinc in situ, the

dimensions of saidchamber being suchthat no portiondsaidiormamidewilibemorethanonehalf inch from said inner walls.

5. A process for eiiecting the catalytic formation of hydrocyanic acid comprising passing 5 iormamide over a heated metal surface having a thin adherent coating of a catalytic oxide or a metal selected from the group consisting of zinc, aluminum, manganese, chromium and tin, said coating having been produced by coating said 10 surface with said metal and subsequently oxidizing the coated surface.

6. A process for eiifecting the catalytic formation of hydrocyanic acid comprising passing iormamide over a heated metal surface having 15 a thin adherent coating of a catalytic oxide of a metal selected from the group consisting of zinc, aluminum, manganese, chromium and tin, said coating having been produced by electroplating said surface with said metal and subsequently an oxidizing the electroplated surface.

'1. A process for eiiecting the catalytic formation 0! hydrocyanic acid comprising passing Iormamide over a heated metal sin-lace having an adherent coating 01' zinc oxide formed by 25 oxidizing an adherent electroplated film-oi zinc.

HARLAN A. BOND. NORMAN D. SCOTT. 

